linux-kernel - Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests

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Date:   Fri, 14 Oct 2016 15:51:34 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     david.vrabel@...rix.com, JGross@...e.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        roger.pau@...rix.com
Subject: Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH
 guests

On Fri, Oct 14, 2016 at 03:43:19PM -0400, Boris Ostrovsky wrote:
> On 10/14/2016 03:19 PM, Konrad Rzeszutek Wilk wrote:
> > On Fri, Oct 14, 2016 at 02:05:16PM -0400, Boris Ostrovsky wrote:
> >
> > Perhaps add in here:
> >
> > PVH is like PV in that there are no PCI devices - which HVM
> > code would piggyback on to find the Xen PCI platform device and
> > use its MMIO space to stash the grants in.
> >
> > For PVH we balloon out memory and stash the grants in there.
> >
> > (Which begs the next question - where and when do we balloon out the
> > normal memory back in?)
> 
> Are you saying that we should get back memory that we gave to grant tables?

Yes.

In pure HVM that area is MMIO - which hvmloader has balloonned out.

The hvmloader then balloons that number of pages back  at the end of
guest memory (after 4GB).